Characterization of TaFe_1.25Te₃, a new layered telluride with an unusual metal network structure

The new layered material, TaFe_1+xTe₃ (0.25 <x <0.29), has been synthesized by reaction of the constituent elements. Single-crystal X-ray diffraction studies show that at x = 0.25 the compound crystallizes in the space group P2₁ m (no. 11) (a = 7.436(1), b = 3.638(1), c = 10.008(1) Å, β = 109.17(1)°). The structure features an unusual TaFe bonded network that contains an equal number of Ta and Fe atoms. The metal network lies between tellurium layers, forming a FeTaTe₃ "sandwich." Additionally, x Fe atoms per formula unit partially occupy a square pyramidal site that provides interlayer bonding through the apical tellurium, which is in an adjacent "sandwich." Selected area electron diffraction studies did not reveal any order in the partially occupied Fe positions. Electrical and magnetic measurements reveal that, at x = 0.25, the compound is an antiferromagnetic metal (T_N = 200 K) and undergoes a structural phase transition at 1010 K.